1. Field of the Invention
The present invention relates to a method for reducing a thickness of an interfacial layer, a method for forming a high dielectric constant gate insulating film, a high dielectric constant gate insulating film, a high dielectric constant gate oxide film, and transistor having a high dielectric constant gate oxide film, particularly relating to a method for controlling a structure of solid interface, and to a structure of a gate stack.
2. Description of the Related Art
Along the trends for miniaturizing elements on an integrated circuit, as a gate insulating film, an oxide film of high dielectric constant, such as HfO2 and La2O3, has been used, replacing the conventionally used silicon oxide.
When such high dielectric oxide film is formed on a substrate of Si or Ge, an interfacial layer, such as SiOx and GeOx, is formed at the interface between the oxide film and the substrate to lower the effective dielectric constant, which is recognized as a problem. An interfacial layer is formed within a film when a film forming process is performed at high temperature. Even when a high dielectric film is deposited at low temperature, an interfacial layer is still formed by oxygen supplied through the high dielectric film during annealing performed later.
As for such a high dielectric film, for example, HfO2 is used. There has been an attempt to further increase its dielectric constant by adding Ti to HfO2 (for example, Min Li, Zhihong Zhang, Stephen A. Campbella, Hong-Jyh Li and Jeff J. Peterson, “Hafnium titanate as a high permittivity gate insulator: Electrical and physical characteristics and thermodynamic stability,” JOURNAL OF APPLIED PHYSICS 101, 044509 (2007)), but it does not substantially solve the aforementioned problem associated with the interfacial layer.
In the past, there was a research where La2O3 was laminated as a capping layer on HfO2 (for example, H. N. Alshareef, M. Quevedo-Lopez, H. C. Wen, R. Harris, P. Kirsch, P. Majhi, B. H. Lee, R. Jammy, D. J. Lichtenwalner, J. S. Jur, and A. I. Kingon, “Work function engineering using lanthanum oxide interfacial layers,” APPLIED PHYSICS LETTERS 89, 232103 (2006)). This related art is however to control the threshold voltage by varying the effective work function of the electrode, not to solve the aforementioned problem associated with the interfacial layer.
Further, there has been an attempt for preventing migration of oxygen by capping HfO2 with Al2O3 deposited thereon (for example, Manisha Kundu, Noriyuki Miyata, Toshihide Nabatame, Tsuyoshi Horikawa, Masakazu Ichikawa and Akira Toriumi, “Effect of Al2O3 capping layer on suppression of interfacial SiO2 growth in HfO2/ultrathin SiO2/Si (001) structure,” APPLIED PHYSICS LETTERS VOLUME 82, NUMBER 20, 19 MAY 2003). Since this related art is to prevent oxygen from being diffused from outside of the oxide to the inside thereof, it cannot solve the aforementioned problem by the capping, once the interfacial layer is formed (as described above, an interfacial layer is easily formed).
Furthermore, there has been an attempt for absorbing oxygen from an interfacial layer present below a high dielectric film through the high dielectric film by capping the high dielectric film of HfO2 or the like with Ti, or AlN deposited thereon (for example, H. Kim, et al., “Engineering Chemically Abrupt High-k Metal Oxide/Silicon Interfaces Using an Oxygen-Gettering Metal Overlayer,” JOURNAL OF APPLIED PHYSICS 96, 3467 (2004), and M. P. Agustin et al., “Influence of AlN layers on the interface stability of HfO2 gate dielectric stacks,” APPLIED PHYSICS LETTERS 89, 041906 (2006)). By withdrawing oxygen from the interfacial layer in this manner, however, oxygen is also withdrawn from the high dielectric film, which increases oxygen voids in the high dielectric film. The presence of the oxygen voids in the high dielectric film becomes a factor for deteriorating reliability of a device, and therefore it is not preferable to solve the aforementioned problem of the interfacial layer using this method.
In the case of a III-V compound semiconductor such as GaAs, there is a problem that numbers of interface defects are formed at an interface between the high dielectric film and GaAs, and layers of Si/SiNx, Ge, and Ga2O3 are intentionally inserted to prevent such interface defects (for example, M. Passlack, et al., “Interface charge and nonradiative carrier recombination in Ga2O3-GaAs interface structures.” JOURNAL OF VACUUM SCIENCE & TECHNOLOGY, B17(1), Jan/Feb 1999, Davood Shahrjerdi, et al., “Unpinned metal gate/high-k GaAs capacitors: Fabrication and characterization,” APPLIED PHYSICS LETTERS 89, 043501 (2006), and Masamichi Akazawa, et al., “Capacitance-voltage and photoluminescence study of high-k/GaAs interfaces controlled by Si interface control layer” JOURNAL OF VACUUM SCIENCE & TECHNOLOGY, B27(4), Jul/Aug 2009). When these inserted layers are oxidized (when an oxide layer is originally inserted, the oxide layer itself), the same problem as mentioned above is caused so that improvement in properties of a device produced from these semiconductors is inhibited.